This invention relates to a tubular cutting tool, namely a device for remotely cutting tubulars, such as well casings, drill pipes and underwater or buried pipes, from the inside, using an electrically driven cutting head.
During certain phases of well drilling and development it is necessary to recover metal tubulars, or sections thereof, from the borehole. In order to achieve this, a device must be lowered inside the tubular, then operated remotely to perform a cut. The devices commonly employed in the art for this purpose can be largely divided into two categories.
The first category encompasses explosive or “chemical cutting” devices which are deployed on a cable, wireline or electric line. Examples of such devices are described in U.S. Pat. Nos. 5,129,322 and 4,125,161. These devices suffer from logistical and operational difficulties and impediments arising from the additional safety precautions required when utilising explosives and corrosive chemicals.
The second category consists of mechanical or hydraulic cutting devices which are deployed on the end of drill pipe, coiled tubing or other tubular; examples of such cutting devices are to be found in European Patent Application No. 0 266 864 and U.S. Pat. No. 3,859,877. Such devices suffer from the disadvantage of being cumbersome, as well as expensive to purchase, deploy and operate; the operation and deployment of the devices commonly requires a complete drill rig. Furthermore, in situations where the tubular to be cut is narrow employment of devices in this category may be precluded. Typically, devices in this category incorporate a number of large blades which gouge their way through the tubular. Gouging a cut through the tubular, rather than performing a precision cut, suffers from the disadvantage of requiring a large amount of energy as well as producing long “apple peel” spirals of metal which can fall into the tubular and hinder the cutting operation as well as future operations on the cut tubular.
In general, even tubular cutting tools incorporating more than one blade to perform a precision cut, rather than gouging a cut, suffer from the disadvantage that multiple blades have a tendency to “skip” in and out of the individual cuts they produce, resulting in an increased propensity for the blades to snap; in a single bladed tool, the single cutting blade runs around the wall of the tubular in its own cut, even in a slight eccentric or angled deployment.
In addition to the disadvantages already discussed, devices in both categories typically leave the cut end of the tubular in a ragged condition, which can occlude subsequent operations involving the tubular. Furthermore, those devices in both categories which include a mechanism for anchoring the device within a tubular, typically utilise some form of hydraulic or pneumatic means for part of the deployment of that mechanism. The use of hydraulic and/or pneumatic means results in the devices requiring multiple cables/hoses which can lead to additional deployment problems when the device is to be used in a tubular, for example, a live oil well, having a seal and airlock mechanism and/or when a cut is to be made at great depth.